Underground storm shelters provide significantly improved defences from the hazards of a tornado or hurricane. Building one for your family is important particularly if you live in areas that are historically tornado prone. You can make a do-it-yoursel underground shelter as an inexpensive option, constructed with simple materials like wood, breeze blocks and sheet metal.
Draft a diagram using graph paper and a geometry kit while deciding on some key design element choices. Your shelter needs sturdy walls, a floor, a roof and a heavy-duty door and entrance staircase. Fully underground versions will required a powered air ventilation system, which can add a greater degree of complexity and become potentially dangerous in the event of a power failure or extended emergency. The easiest underground designs for the DIY enthusiast are Berm storm shelters. They avoid the need for powered ventilation by having an above-ground roof and air vents, and a below-ground waiting area. The downside of the Berm design is that they aren't quite as resilient as underground designs unless you incorporate a heavy-duty steel roof and siding plates.
Call your local utility companies and determine the location of all your power, gas and water lines. Keeping these details in mind, mark out the location of your storm shelter. The ideal place is under a covered joined garage or basement, however, altering already lain foundations can be problematic. Nearly as good is building the shelter in the lee of your house, near an exit.
Use a pickaxe if necessary to break up rough earth before removing shovelling out the cellar in the shape you want. Be sure to include the width of the bricks in your diagram in the measurements for the hole. Dig a rough ramp shape leading into the main hole. This is where you'll build up your stairway. Alternatively, if space is an issue, a ladder entry also works as long as you have no mobility impaired persons in your home.
Dig post holes around the perimeter of the shelter, at roughly one-meter intervals. Be sure to position the holes far enough away from the edges of the hole to allow you to lay breeze blocks on the outside of each 4-by-4 post. Insert 4-by-4 treated posts into the holes, supporting them with temporary 2-by-4 supports to keep the posts level and facing upwards. Mix your concrete with water, as per the package instructions, and pour into the post holes. Allow the cement time to set as outlined by the package instructions. Using metal pegs, fix a PVC water barrier to the outside and bottom of the holes for basic water protection.
Mix and prep the breeze block mortar and construct the outer wall; use a varied pattern so that the centre of the block above is covering the joining gaps of the blocks below. Don't be afraid to use the hammer and chisel to break edge bricks into shape if they don't fit quite properly. Be sure to construct the walls of the stairway, or ladder entrance, now as well using the same method.
Lay down the patio stones for the floor of the shelter. Use the chisel and hammer to break away chunks of the cement to allow the patio stones to snugly meet the walls and edges of the posts. Use the same mortar from the wall-building process to fill the gaps in the floor and allow the structure to dry to the mortar specifications on the packaging. Lay additional pieces of patio stone to create a floor for your ladder bay or to make stairs. To make stairs, simply break and stack patio stones until you reach the desired shape, using mortar to hold it all together.
Attach cross beams to the main support posts using mortise and tenon joinery, fixing the beams in place with wood screws. To make a mortise and tenon joint use a jigsaw to cut a peg and socket shape into the beams respectively. The final shape is similar to the way pieces of a jigsaw puzzle fit together. A mortise and tenon joint is the strongest way to join wood. Cover the roof in steel plates, joining them to the post beams and to the cross beams by drilling through them with a heavy bit and running heavy-duty nuts and bolts. Be sure to use wide steel washers to make the joints strong and spread the strain across the wood. Tighten the bolts as much as possible using a wrench and a pipe for extra leverage. If your design is fully underground, install your prefabricated ventilation system now, as well as the prefabricated heavy duty steel door. If you used a Berm design install the prefabricated heavy duty vents along the exposed section of the side walls, as well as the door and possibly ladder.
Check local building codes and ensure your design meets all guidelines. Pick dense, high-quality treated hardwood for your posts and crossbeams for added strength. Set up an emergency kit and store it in your shelter to make the stay more comfortable because you could be there for a while. Don't forget to add seating and cots.
Don't build underground shelters on a flood plain. If you are unsure if your area is prone to flooding, consult local authorities. Flood-prone area residences should instead contain a safe room in the core of the building.